The present invention is directed to a method for determining the product of two numbers and an apparatus for carrying out that method.
In a computing system employing solid state components, preferably constructed from silicon components arrayed on a substrate, certain basic design criteria generally apply. For example, it is desired that the least space possible upon the substrate be occupied by each component. Further, it is desired that energy consumed by the apparatus be minimized as much as possible, especially in battery-supplied systems. Also, it is desired that the computing system operate as speedily as possible.
A multiplier for such computing systems is generally fashioned of a matrix of switching transistors, which matrix is of sufficient size to accommodate the maximum expected size of numbers to be handled by the computing apparatus. Thus, for example, in order to have a multiplication of a 4-digit number by a 4-digit number, a multiplier would necessarily comprise a 16.times.16 bit matrix (i.e., 16 columns of transistors, each column having 16 rows of transistors) with additional rows, or columns, or both to accommodate carries and other overhead operations involved in multiplication.
For smaller numbers, higher significance bits within the multiplier matrix are zero-filled as appropriate to correctly store the multiplicand and the multiplier involved in the multiplication operation. However, those zero-filled bits must still be powered-up in order to effect such zero-filling. Such zero-filled bits are necessarily involved in the calculations effected by the multiplier, so speed of operation, power requirements, and "real estate" (i.e., space) occupancy on the substrate are all sacrificed in accommodating larger numbers for multiplication operations.
It would be advantageous to have a multiplier which only powers-up a sufficient number of bits necessary for a specific multiplication operation to conserve power, especially in a battery-supplied system. It would be further advantageous to have a multiplier which occupies as little "real estate" as possible on the substrate in order to conserve space and enhance packaging of a system employing the multiplier. It would be still further advantageous to have a multiplier which speedily effects multiplication operations to enhance the operational speed of a system employing the multiplier.
It would also be advantageous to effect multiplication by a method which facilitates design and operation of a multiplier which can realize the above-described desired advantages.